This thesis studies the general heat conduction law, irreversible thermodynamics and the size effect of thermal conductivity exhibited in nanosystems from the perspective of recently developed thermomass theory. The derivation bridges the microscopic phonon Boltzmann equation and macroscopic continuum mechanics. Key concepts such as entropy production, temperature and the Onsager reciprocal relation are revisited in the case of non-Fourier heat conduction. Lastly, useful expressions are extracted from the picture of phonon gas dynamics and are used to successfully predict effective thermal conductivity in nanosystems.

Dr. Dong received his B. S. in Mechnical Engineering in 2008 and Ph. D. degree in Engineering Physics in 2014, both from Tsinghua University.

His research areas are focused on:

1. Nano-scale Heat Transfer: Develop a generalized heat conduction law based on the thermomass theory and the phonon Boltzmann equation, which can predict the nanoscale heat conduction.
2. General Theory for Transport Process and Non-equilibrium Thermodynamics: Revisit the non-equilibrium thermodynamics based on the thermomass theory, Propose a new picture for the entropy production and Onsager reciprocal relations.

AWARDS/HONORS

1. First Class Award for Outstanding PHD Thesis of Tsinghua University 2014 (25 of 889 Graduated PHD students)
2. Wu Zhonghua Scholarship for graduates 2012 (13 in the Society of Engineering Thermophysics of China)
3. First Class Comprehensive Scholarship for graduates 2013 and 2011
4. First Class Award for Outstanding Youth Conference Paper in Annual Conference of Chinese society of Engineering Thermophysics, Heat and Mass Transfer 2011 (Only 2 for over 600 Papers)
5. Outstanding Graduates of Tsinghua University 2008 (56 of 3044 Students)

PUBLICATIONS

[1] Y. Dong, B.Y. Cao and Z. Y. Guo. Ballisticdiffusive phonon transport and size induced anisotropy of thermal conductivity of silicon nanofilms. Physica E: Low-dimensional Systems and Nanostructures, 66, 1 (2015).
[2] Y. Dong and Z. Y. Guo. Hydrodynamic modeling of heat conduction in nanoscale systems. Journal of Nanoscience and Nanotechnology, 15, 3229 (2014)
[3] Y. Dong, B.Y. Cao and Z. Y. Guo. Size dependent thermal conductivity of Si nanosystems based on phonon gas dynamics. Physica E: Low-dimensional Systems and Nanostructures, 56, 256 (2014).
[4] Y. C. Hua, Y. Dong and B. Y. Cao. Monte Carlo simulation of phonon ballistic diffusive heat conduction in silicon nano film. Acta Physica Sinica, 62(24), 244401 (2013). (In Chinese)
[5] Y. Dong, B.Y. Cao and Z. Y. Guo. Temperature in nonequilibrium states and non-Fourier heat conduction. Physical Review E, 87, 032150 (2013).
[6] Y. Dong. Clarification of Onsager Reciprocal Relations Based on Thermomass Theory. Physical Review E, 86 062101 (2012).
[7] Y. Dong, B.Y. Cao and Z. Y. Guo. General expression for entropy production in transport processes based on the thermomass model. Physical Review E 85, 061107 (2012)
[8] Y. Dong and Z. Y. Guo. The modification of entropy production by heat condution in non-equilibrium thermodynamics. Acta Physica Sinica, 61(3), 030507 (2012). (In Chinese)
[9] Y. Dong and Z. Y. Guo. From Thermomass Theory to Kinetomass Theory. Journal of Engineering Thermophysics, 33, 465 (2012). (In Chinese)
[10] Y. Dong, B. Y. Cao and Z. Y. Guo. Generalized heat conduction laws based on thermomass theory and phonon hydrodynamics. Journal of Applied Physics, 110, 063504 (2011).
[11] Y. Dong and Z. Y. Guo. Entropy analyses for hyperbolic heat conduction based on the thermomass model. International Journal of Heat and Mass Transfer, 54, 1924 (2011).
[12] X.T. Cheng, Y. Dong, X.G. Liang. Potential entransy and potential entransy decrease principle. Acta Physica Sinica, 60(11) 114402 (2011). (In Chinese)
[13] Y. Dong and Z. Y. Guo. Entropy Analysis in the Heat Wave Propagation. Journal of Engineering Thermophysics, 32, 1889 (2011). (In Chinese)
[14] Y. Dong, G. Chen. On the effective media approximation for thermoelectric properties of composites. 4th International Symposium on Micro and Nano Technology. 8-12, Oct., 2013, Shanghai, China.
[15] Y. Dong, Z. Y. Guo. Theoretical study on the non-Newtonian behavior of simple fluids. 8th International Conference on Flow Dynamics, 9-11, Nov., 2011, Sendai, Japan.

Introduction.- Dynamical governing equation of Non-Fourier Heat Conduction.- General Entropy Production based on Dynamic Analysis.- Non-Equilibrium Temperature in Non-Fourier Heat Conduction.- Dynamic Analysis of Onsager Reciprocal Relations (ORR).- Dynamical Analysis of Heat Conduction in Nanosystems and Its Application.- Conclusion.